1. Field of the Invention
This invention relates to a vehicle seat designed to control a so-called submarine phenomenon, i.e., forward motion the occupant wearing the seat belt may undergo at, for example, an emergent halt of the vehicle.
2. Description of the Related Art
Most vehicle seats have a three-point holding seat belt configured to hold the occupant at three points, i.e., the left or right shoulder, the left side of the waist, and the right side of the waist. The three-point holding seat belt has an upper-half webbing (i.e., shoulder webbing) and a lower-half webbing (lap webbing). The upper-half webbing may be wrapped around the occupant and extend from one shoulder to the left and right sides of the waist, and the lower-half webbing may be wrapped around the occupant's waist and secured. The webbings thus cooperate to hold the occupant to the vehicle seat.
If the vehicle is abruptly decelerated, is suddenly stopped or collides with the vehicle running before it, inertia will act on the occupant to move him or her forward. In most cases, the seat belt prevents such a forward motion of the occupant, in spite of the inertial force generated in such an event. However, the seat belt may fail to function well if the occupant undergoes a so-called submarine phenomenon, in which the occupant's buttocks slide forwards on the seat, while sinking in the seat cushion.
A configuration is known, which is designed to control the submarine phenomenon (i.e., forward motion of the buttocks of the occupant wearing the seat belt, at such an emergency). In this configuration, a control member extends beneath the seat pad, between the left and right side frames, and below that part of the seat cushion which is almost at the middle in the fore-to-aft direction of the vehicle. The control member is positioned low, making the occupant feel comfortable. At an emergency, the control member rises, pushing up the seat pad in front of the occupant's buttocks. So pushed up, the seat pad controls the submarine phenomenon.
JP 2002-046513A, for example, discloses a vehicle seat, in which a cross member having a foldable part extends between the left and right side frames of the seat cushion. The foldable part of the cross member is bent with the pressure the occupant applies to the cross member. When the occupant's buttocks move forward at an emergency, however, the foldable part rises, pushing up the seat pad and thus controlling the submarine phenomenon.
Further, JP 2004-237820A discloses a vehicle seat, in which an elastic band used as control member extends beneath the seat pad and between the left and right side frames of the seat cushion. A traction device having an inflator is connected to an end of the elastic band hanging along the side frames. At an emergency, the inflator causes the traction device to pull the ends of the elastic band in both the leftward direction and the rightward direction. The traction device therefore stretches the elastic band between the side frames, pushing up the seat pad at the lower surface. As a result, the seat pad rises in front of the occupant's buttocks, controlling the submarine phenomenon.
In the vehicle seat disclosed in JP 2002-046513A, the cross member is hard, formed of, for example, a steel plate. Therefore, if the cross member is positioned near the upper surface of the seat pad, it can push the seat pad upwards much enough to control the submarine phenomenon at an emergency. While the vehicle is running in normal state, however, the occupant perceives the existence of the cross member and feels somewhat uncomfortable. In order to make the occupant comfortable while the vehicle is running in normal state, the cross member may be arranged above the seat pad. If so arranged, however, the cross member cannot push up the seat pad sufficiently, possibly failing to control the submarine phenomenon at an emergency.
In the vehicle seat disclosed in JP 2004-237820A, an elastic band, such as elastomer sheet, is used as control member. The band can hardly be perceived through the seat pad even while the vehicle is running in normal state. Since the band is arranged on the lower surface of the seat pad, it is sufficiently spaced from the upper surface of the seat pad. This ensures comfort to the occupant. At an emergency, the traction device pulls the band, fast stretching and lifting the band. The band can therefore sufficiently control the submarine phenomenon.
A type of a vehicle seat is known, which comprises a seat cushion and a seat lifter. The seat lifter includes a pair of front links and a pair of rear links. All links (i.e., height links) extend between, and are coupled to, side frames and a car-floor side support member. The seat lifter can therefore move the seat cushion up and down.
The elastic band extending between the side frames of the seat cushion is used as control member and is stretched by the traction device mounted between the left and right support member. This configuration will be complicated if the seat cushion is moved up and down.
That is, in the vehicle seat having a traction device secured to the support member, the distance between the seat cushion and each support member will change as the seat lifter moves the seat cushion up or down. More precisely, the distance between the top of side frame and the traction device will change. The band will change in length because it extends between the side frame and the traction device and hangs along the side frame.
Therefore, the band must be fed (to lift the seat cushion) or pulled (to lower the seat cushion) and must thereby be adjusted in length immediately at an emergency, regardless of the position the seat cushion assumes. Unless the length of the band is precisely adjusted as the seat cushion is lifted or lowered, the band is pulled, pushing up the seat pad and inevitably making the occupant feel uncomfortable, while the vehicle is running in normal state. At an emergency, the band may be stretched with some delay, possibly failing to control the submarine phenomenon.
It is not easy to adjust the length of the band as the seat cushion is lifted or lowered. The band, which is pulled or stretched to control the submarine phenomenon, needs to be secured to the seat cushion only (more precisely, to the side frame of the seat cushion), no matter whether the vehicle seat has a seat lifter or not. The position of the traction device is inevitably limited.
Further, the band must be stretched without twisting, to pull up the seat pad on an emergency, at the part lying in front of the occupant's buttocks, thereby to control the submarine phenomenon. If the band twists as it is pulled, it cannot reliably transmit a pushing force to the seat pad even if it is well stretched. If this is the case, the seat pad can hardly be pulled up to assume a specific shape, and the submarine phenomenon may not be controlled.
The band can be stretched without twisting if it is pulled in the direction it extends between the left and right side frames. In the vehicle seat disclosed in JP 2004-237820A, the traction device is arranged below the band and in parallel to the band. Thus, the traction device pulls the band in the same direction the band extends.
In order to pull the band in the direction the band extends, the position of the traction device is limited.